Plasmons are quasiparticles resulting from the quantization of plasma oscillations, just as photons and phonons are quantizations of light and sound waves, respectively. Surface plasmons are those plasmons that are confined to surfaces and that interact strongly with light. They occur at the interface of a vacuum or material with a positive dielectric constant with that of a negative dielectric constant (usually a highly conductive material such as a metal or doped dielectric). Plasmonics is a field where one exploits the short wavelength of a surface plasmon in an analogous method as one exploits an optical wavelength for information transfer or data manipulation. But, rather than a quantum of light (a photon), a plasmon or collective excitation in the electron density is used.
Standoff detection is a detection method that can be used to identify dangerous solvents, chemicals, and explosives at safe distances from people and vital assets, in order to reduce the potential for severe damage. Standoff methods focus on chemical identification to detect explosives, breakdown products, and/or other precursors. Some of the major challenges for standoff detection include developing new methods that enable classification and identification of new and emerging threat chemical signatures from a distance. Correlation spectroscopy is one such method that could be used for standoff detection.
Correlation spectroscopy is a method used for sensing and analysis applications. The method consists of finding a correlation between the transmission of an unknown sample and the transmission of a reference cell that contains a known compound. Correlation spectroscopy works well for materials such as gases, because they exhibit narrow absorption bands and small modulations of the transmission of the reference cell can result in a large modulation on a beam. But for gases that are dangerous or hazardous, the use of correlation spectroscopy requires that a references cell that contains a dangerous material be proximate to the user, which is an undesirable situation.
A correlation spectrometer that is based on surface plasmon resonance could obviate the need for multiple reference cells containing the compounds of interest. This would obviate the need for the user to come into close contact with dangerous solvents, chemicals or explosives such as chemical-warfare agents present within a reference cell; it would also obviate the need to store a multitude of reference cells containing hazardous substances. In sum, plasmonic correlation spectrometers could overcome the disadvantages of the prior art.
In view of the above, it is an object of the present invention to provide a plasmonic correlation spectrometer that uses a plasmonic array in place of a reference cell for operation. Another object of the present invention is to provide a plasmonic correlation spectrometer with a greatly reduced size. Still another object of the present invention to provide a plasmonic correlation spectrometer that is amenable to fabrication on the chip scale for integrated photonic devices. Yet another object of the present invention to provide a plasmonic correlation spectrometer for standoff detection of hazardous materials that is much safer to use. Another object of the present invention to provide a plasmonic correlation spectrometer that is configured for the detection of more than one hazardous material at the same time.